a couple of other tips as well:
the placing timer can be funky - so be sure to wait a week after you've either placed or traded the house before you resize (you could get stuck with not being able to replace for x more hours)
before you start, click on the housing tool and mock place a house - that is, pick a house type till you get a footprint. If the housing server is down, you'll get a msg saying so - obviously don't resize your house if you get this msg, because it will let you bring your house down but will not allow you put it back up.
The spot you are working in is bound to your account for a hour and after that it's free game - also don't try too many times to resize or you may be locked out for too many tries.
It does work really well but you do have to be extra cautious before you start.